1. Field of the Invention
The invention relates to a light emitting diode (LED) device. More particularly, it relates to an LED device including LED chips of two or more types having different light source colors that are combined as light sources to provide a light of a desired tone by mixing the light emitted from the various LED chips.
2. Description of the Related Art
A spectrum of light emitted from an LED chip has a sharp rise and fall, which provides a light source color of a tone approximately corresponding to a peak emission wavelength in a spectral distribution. An LED light source having such an optical property may be employed in a method to provide a light of a tone different from the light source color. In this method, LED chips of two or more types having different light source colors are generally combined to provide a light of a desired tone by mixing light emitted from the LED chips.
An example of the above-described related art LED device is shown in FIG. 9. This is also referred to as a shell type LED device, in which three lead frames 51R, 51G, 51B having recessed tips formed as cups with reflecting inner circumferential surfaces, and three lead frames 52R, 52G, 52B having flat tips, are arranged in parallel, leaving a certain interval therebetween.
On the bottoms of the cups in the three lead frames 51R, 51G, 51B, a red LED chip 53R, a green LED chip 53G and a blue LED chip 53B having light source colors of red, green and blue are mounted. The red LED chip 53R has a lower electrode, which is electrically brought into conduction with the lead frame 51R for receiving the red LED chip 53R mounted thereon. The red LED chip 53R has an upper electrode, which is connected via a bonding wire with the tip of the flat tip lead frame 52R to be electrically in conduction therewith.
Of the pair of electrodes formed on each of the green LED chip 53G and the blue LED chip 53B, one is connected via a bonding wire with the lead frame 51G and 51B, respectively, for receiving the corresponding LED chip mounted thereon, and electrically brought into conduction therewith. The other of the pair of electrodes formed on each of the green LED chip 53G and the blue LED chip 53B is connected via a bonding wire with the tip of the flat tip lead frame 52G and 52B, respectively, and electrically brought into conduction therewith.
The tips of all the lead frames 51R, 51G, 51B, 52R, 52G, 52B are sealed in a light transmissive resin, and the red LED chip 53R, the green LED chip 53G, the blue LED chip 53B and the bonding wires are protected with the sealed resin 54. The light exit surface of the sealing resin 54 is formed with three semispheroidal convex lenses 55 having optical axes substantially coincident with those of the red LED chip 53R, the green LED chip 53G and the blue LED chip 53B.
Each of the red, green and blue light emitted from respective LED chips is partly guided in the light transmissive resin of the sealed resin to directly travel toward a respective semispheroidal convex lens on the light exit surface. On the other hand, each light is partly reflected at a respective inner circumferential surface of the cups in the lead frame, and the reflected light is guided in the light transmissive resin to travel toward a respective convex lens. When the light reaches the convex lens after passing through these two optical paths, the light is distributed to achieve certain directivity through the convex lenses on the light exit surface and is externally emitted (emitted into the atmosphere).
The red light, the green light and the blue light, or the three primary colors of light, emitted from the light exit surfaces of the respective convex lenses are mixed to form a white light.
Mixing the light emitted from the respective red LED chip, green LED chip and blue LED chip while selectively controlling (including blinking) the amounts thereof can yield a light of substantially all colors including the light source colors of the respective LED chips and white light (see Patent Document 1: JP-A 10-173242, for example).
As desire for downsizing and thinning electronic instruments and lowering prices thereof has proceeded in recent years, similar requirements/characteristics are desired for the electronic components and mounting boards contained in the electronic instruments. Therefore, a printed wire board for use in an electronic components mounting board is designed as a single-sided board having printed wire patterns formed only on one surface of the printed wire board to arrange mounted components intensively on one surface. Electronic components of the surface-mount type are mounted on the same surface of the single-sided board on which the wire patterns are formed to achieve a lowered height and a lowered cost of the electronic components mounting board.
However, the above-described related art LED device can not typically be mounted on the same surface of a single-sided board on which surface-mount electronic components are mounted. Therefore, mounting these related art LED device on the printed wire board, mixed with the surface-mount electronic components, often requires the use of a double-sided board having wire patterns formed on both surfaces of a printed wire board. In this case, the LED device is mounted on the surface of the double-sided board opposite to the surface on which the surface-mount electronic components are mounted.
Accordingly, the height of the electronic components mounting board is increased and the cost of the printed wire board is elevated, which in turn elevates the cost of the electronic components mounting board and electronic instrument itself. This result runs counter to the above-described desire for a less expensive, thinner electronic component.
To achieve a certain amount of downsizing and/or thinning of the electronic instrument as well as lowering costs/prices thereof, surface-mount LED devices shown in FIGS. 10 and 11 which have the optical action similar to that of the related art shell type LED device can generally be employed.
In the surface-mount LED device of the related art shown in FIG. 10, LED chips 61 are mounted in a plurality of recessed cups 62 formed in a lead frame 63 that is insert-molded in a white resin that has high reflectivity. Above the cups, a cavity 66 having an inner circumferential surface that is open wider at an upward location is formed in a reflector 64 to configure a package.
An LED chip 61 is fixed in each cup 62 via a conductive member (not shown). The LED chip 61 has a lower electrode, which is electrically brought into conduction with the lead frame 63. The LED chip 61 has an upper electrode, which is connected and electrically brought into conduction via a bonding wire 65 with a lead frame 63′ separated from the lead frame 63.
A light transmissive resin 67 is filled in the cavity 66 and in a space between the cup 62 and the LED chip 61 to protect the LED chip 61 and the bonding wire 65 with the sealed resin. At the same time, convex lenses 68 having optical axes substantially coincident with those of the LED chips 61 are formed on the light exit surface of the sealed resin.
The other surface-mount LED device of the related art shown in FIG. 11 is configured without the white resin located below the lead frame 63 from the LED device shown in FIG. 10. In a word, the part above the lead frame 63 has the same configuration and the same optical action as that of the LED device shown in FIG. 10.
The lead frame for use in the above-described surface-mount LED device is produced through pressing a flat metal plate using a press mold. At that time, the mold structurally determines the shortest interval between adjacent cups based on the thickness of the lead frame. Therefore, the shortest distance between adjacent LED chips mounted on the cups is limited as determined by the thickness of the lead frame.
In such a case, when plural LED chips having different light source colors are mounted in respective cups to mix the light that is emitted from the LED chips, the LED chips may not be located sufficiently close to each other for a particular purpose or application. As a result, the LED device may result in an insufficient light mixture and/or a deteriorated color mixture, etc.
A constraint on the interval between the cups also exerts an influence on the ability to downsize the LED device, often resulting in insufficient downsizing.
The lead frame is produced through pressing of a flat metal plate. Accordingly, physical properties such as the hardness of the metal plate and characteristics such as the thickness add constraints to the shape of the lead frame, such as the inner diameter and depth of the cup. Therefore, the flexibility of the optical design associated with the LED device is limited, and the optically and structurally ideal best product can not be made.
It is difficult work to form the cup integrally with the circuit pattern composed of the flat metal plate such that it has an extremely narrow width. In this case, elevation of the mold production cost due to the complicated press mold and insufficient dimension accuracy may invite elevation of the production cost and deterioration of quality.